2003 Z71 Tahoe intermittent battery drain

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Hutch123

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New to this forum. I'm sure the 03 battery drain has been discussed before but I couldn't rewlly find the answer I'm looking for. I have an 03 z71 tahoe. A few months ago it started killing batterys overnight. This is intermittent. Sometimes it does somtimes it doesn't. I have replaced 2 battery now. I have recently fixed the engine block ground, put in a new BCM. the battery is charged by the alternator just fine. Everything appears to shut off after vehicle is turned off and door is shut. I have tried to do a parasitic drain test and all I see is 12-14 mili amps. I'm not sure how to diganose this issue.
 

HiHoeSilver

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New to this forum. I'm sure the 03 battery drain has been discussed before but I couldn't rewlly find the answer I'm looking for. I have an 03 z71 tahoe. A few months ago it started killing batterys overnight. This is intermittent. Sometimes it does somtimes it doesn't. I have replaced 2 battery now. I have recently fixed the engine block ground, put in a new BCM. the battery is charged by the alternator just fine. Everything appears to shut off after vehicle is turned off and door is shut. I have tried to do a parasitic drain test and all I see is 12-14 mili amps. I'm not sure how to diganose this issue.

One thing you can try is to pull fuses one by one while your meter is on the battery and see if any particular fuse has a noticeable effect.
 

M1Gunner

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There’s quit a few different scenarios our older trucks will drain the battery for... intermittently. 1. BCM starting to fail... 2. Drivers door latch starting to fail... 3. Vanity mirrors switch with powered lights in the sun visors failing... 4. Aftermarket installs... ^^^ as silver stated catch it in the act and start pulling fuses.
 

swathdiver

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William, do you have access to a Tech2 or a scan tool that can pull internal body module codes? The BCM does look for and has codes for parasitic drains. Any work done on your ignition lately? If the ignition lock is not installed right, such can drain the battery too.
 
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Hutch123

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William, do you have access to a Tech2 or a scan tool that can pull internal body module codes? The BCM does look for and has codes for parasitic drains. Any work done on your ignition lately? If the ignition lock is not installed right, such can drain the battery too.

No aftermarket parts and no recent ignition work that I know of. Bought used 3 months ago. New development though. Tonight it went into reduced power mode again which it hasnt done since the new BCM. Also, used my brights tonight for the first time in awhile and the instrument panel lit up like a chrismas tree. Speed and tach shut off and all the scary lights came on. Car even jolted. and then everything went back to normal. Does this almost every time I hit the brights. Related?
 
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Hutch123

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Well, where do you live? Maybe someone nearby has a Tech2 and can lend a hand?
Charleston SC. I'm wondering if my battery cables could be the issue. I just went into a convient store and came back out and the car was completely dead after I just drove over 200 miles!! I thought no way. I wiggled the side mount terminals and nothing changed. I wiggled the battery cables on accident and I heard my open door alarm. Truck started right back up....any thoughts?
 

HiHoeSilver

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Charleston SC. I'm wondering if my battery cables could be the issue. I just went into a convient store and came back out and the car was completely dead after I just drove over 200 miles!! I thought no way. I wiggled the side mount terminals and nothing changed. I wiggled the battery cables on accident and I heard my open door alarm. Truck started right back up....any thoughts?

Change em and see.
 

swathdiver

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Check them for tightness and corrosion and even if you cannot see it, you'll probably be best off replacing them. I've done battery cables on most of the GM cars we've owned since the 1980s.
 

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